MUSICK: SEASONAL DISTRIBUTION OF SIBLING HAKES 



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Figure 1. — Sampling strata where collections were made during the RV Albatross IV 

 groundfish surveys. (After Grosslein, 1969.) 



Yankee otter trawl with a cod-end liner (mesh 

 diameter one-half inch stretched) was towed on 

 the bottom for one-half hour at each station. 

 Towing speed was approximately 3.5 knots. The 

 sampling method and design were described in 

 detail by Grosslein (1969). Length of specimens 

 reported in the present paper is total length 

 unless noted otherwise. 



Factors Analyzed 



Life History Stages 



The following summary of the life histories of 

 U. chuss and U. tenuis is extracted from Musick 

 (1969). Urophycis chuss has pelagic eggs and 

 pelagic larvae that descend to the bottom at a 

 length of about 35 to 40 mm. The young then 

 live within the mantle cavity of the sea scallop, 

 Placopecten magellanicus. The largest U. chuss 

 thus far found inside Placopecten have been 130 

 to 140 mm long. Urophycis chuss becomes 

 mature at about 290 mm in length. The otter 

 trawl used in the present study catches no eggs 

 or larvae and very few pelagic juveniles; there- 

 fore, the life history off/, chuss was divided into 

 three demersal stages defined by length: juvenile, 

 « 14 cm; immature, 15-28 cm; and mature, ^29 cm. 

 Urophycis tenuis has pelagic eggs and pelagic 

 larvae which migrate to the bottom at a length 

 of about 80 mm (or smaller sizes in shallow 

 harbors and estuaries). Urophycis tenuis grows 

 much larger than U. chuss and matures at about 



500 mm in length. The life history can be 

 divided into only two stages by length in the 

 present study because of the notable lack of 

 young fish in the trawl collections: immature, 

 9-50 cm; and mature, 2=51 cm. The biology of these 

 species does not change abruptly in all indi- 

 viduals at a certain size. The size range over 

 which major biological changes occur may be quite 

 broad in populations of these Urophycis, but most 

 of the individuals in the population within the 

 size ranges cited above are also within the cor- 

 responding ontogenetic stage. By classifying indi- 

 viduals into life history stage by size, it is pos- 

 sible to use length-frequency data to determine 

 whether the geographical distribution patterns 

 of species change during ontogeny. 



Natural Divisions of the Study Area 



The survey region was divided into two natural 

 subareas according to topography and hydrog- 

 raphy. The southern New England subarea 

 includes sampling Strata 1 to 19, i.e., the southern 

 parts of Georges Bank, Nantucket Shoals, and 

 the Mid-Atlantic Bight as far south as Hudson 

 Canyon. The Gulf of Maine subarea includes 

 sampling Strata 20 to 40, i.e., the Gulf of Maine 

 including the northern edge of Georges Bank and 

 Browns Bank (Figure 1). 



Topography 



The southern New England subarea is char- 

 acterized by a broad, shallow continental shelf 



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